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 A202868 Array: row n shows the coefficients of the characteristic polynomial of the n-th principal submatrix of the symmetric matrix A115216; by antidiagonals. 3
 1, -1, 1, -6, 1, 1, -11, 27, -1, 1, -16, 78, -112, 1, 1, -21, 154, -458, 453, -1, 1, -26, 255, -1164, 2431, -1818, 1, 1, -31, 381, -2355, 7635, -12141, 7279, -1, 1, -36, 532, -4156, 18390, -45660, 58260, -29124, 1, 1, -41, 708, -6692, 37646, -128190 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS Let p(n)=p(n,x) be the characteristic polynomial of the n-th principal submatrix. The zeros of p(n) are positive, and they interlace the zeros of p(n+1). LINKS Table of n, a(n) for n=1..50. S.-G. Hwang, Cauchy's interlace theorem for eigenvalues of Hermitian matrices, American Mathematical Monthly 111 (2004) 157-159. A. Mercer and P. Mercer, Cauchy's interlace theorem and lower bounds for the spectral radius, International Journal of Mathematics and Mathematical Sciences 23, no. 8 (2000) 563-566. EXAMPLE The 1st principal submatrix (ps) of A115216 is {{1}} (using Mathematica matrix notation), with p(1)=1-x and zero-set {1}. ... The 2nd ps is {{1,2},{2,5}}, with p(2)=1-6x+x^2 and zero-set {0.171..., 5.828...}. ... The 3rd ps is {{1,2,4},{2,5,10},{4,10,21}}, with p(3)=1-30x+57x^2-x^3 and zero-set {0.136..., 0.276..., 2.587...}. ... Top of the array: 1...-1 1...-6....1 1...-11...27...-1 1...-16...78...-112...1 MATHEMATICA f[k_] := 2^(k - 1); U[n_] := NestList[Most[Prepend[#, 0]] &, #, Length[#] - 1] &[Table[f[k], {k, 1, n}]]; L[n_] := Transpose[U[n]]; F[n_] := CharacteristicPolynomial[L[n].U[n], x]; c[n_] := CoefficientList[F[n], x] TableForm[Flatten[Table[F[n], {n, 1, 10}]]] Table[c[n], {n, 1, 12}] Flatten[%] (* A202868 sequence *) TableForm[Table[c[n], {n, 1, 10}]] (* A202868 array *) Table[(F[k] /. x -> -1), {k, 1, 30}] (* A154626 *) Table[(F[k] /. x -> 1), {k, 1, 30}] (* A058922 *) CROSSREFS Cf. A115216, A202605. Sequence in context: A081579 A295707 A146772 * A202877 A174124 A174345 Adjacent sequences: A202865 A202866 A202867 * A202869 A202870 A202871 KEYWORD tabl,sign AUTHOR Clark Kimberling, Dec 26 2011 STATUS approved

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Last modified September 14 10:49 EDT 2024. Contains 375921 sequences. (Running on oeis4.)